There are a number of types of land vehicles equipped with pneumatic tires whose service requirements call for operation on varying terrain, e.g. soft sand, snow and hard surface roads. The traction of these vehicles can be enhanced to match the terrain by adjusting the pressurization of the pneumatic tires. This capability is obtained by equipping the vehicle with an automated system for controlled inflation or deflation of the vehicle tires in response to an operator command.
This type of system is broadly known in the prior art and can take a number of alternative embodiments. A feature typical to many of the embodiments is the use of an air pressure tank or reservoir for supplying air to the vehicle tires in response to an operator command to inflate the tires. However, an air pressure tank and its related pneumatic control circuitry introduce complexity into the system design and add cost and weight to the product.
Similarly, in prior systems the control of air flow is commonly implemented by solenoid relays which open and close valves in response to electrical signals. In order to accommodate the pressures and quantities of air necessary for practical operation of this type of system the solenoid relays must be relatively large, and this is reflected in the cost, size and weight of the pneumatic control circuitry. It is also apparent that use of electrical components in the design of a pneumatic control circuit will also introduce usual concerns of reliability and system complexity.
The following U.S. patents disclose vehicle tire inflation systems of background interest to the present invention: U.S. Pat. Nos. 1,241,696; 1,329,876; 1,855,101; 2,010,150 and 3,099,309.